Turbines are widely used in a variety of aviation, industrial, and power generation applications to perform work. Each turbine generally includes alternating stages of peripherally mounted stator vanes and rotating blades. The stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, and the rotating blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as steam, combustion gases, or air, flows along a hot gas path through the turbine to produce work. The stator vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work.
Each rotating blade generally includes an airfoil connected to a platform that defines at least a portion of the hot gas path. The platform in turn connects to a root that may slide into a slot in the rotor to hold the rotating blade in place. Alternately, the root may slide into an adaptor which in turn slides into the slot in the rotor. At operational speeds, the rotating blades may vibrate at natural or resonant frequencies that create stresses in the roots, adaptors, and/or slots that may lead to accelerated material fatigue. Therefore, various damper systems have been developed to damp vibrations between adjacent rotating blades. In some damper systems, a metal rod or damper is inserted between adjacent platforms, adjacent adaptors, and/or between the root and the adaptor or the rotor. At operational speeds, the weight of the damper seats the damper against the complementary surfaces to exert force against the surfaces and damp vibrations.
Higher operating temperatures generally result in improved thermodynamic efficiency and/or increased power output. Higher operating temperatures also lead to increased erosion, creep, and low cycle fatigue of various components along the hot gas path. As a result, ceramic material composite (CMC) materials are increasingly being incorporated into components exposed to the higher temperatures associated with the hot gas path.
However, as CMC materials become incorporated into the airfoils, platforms, and/or roots of rotating blades, the ceramic surfaces of the rotating blades more readily abrade with conventional metallic dampers. The increased abrasion of the CMC material by the metallic dampers may create additional foreign object debris along the hot gas path and/or reduce the mass of the dampers, reducing the damping force created by the dampers. Therefore, an improved system for damping vibrations in a turbine would be useful.